The invention concerns a bristle for a brush, in particular a cleaning brush, toothbrush or application brush and a method for producing a corresponding bristle of thermoplastic polymers through casting, preferably injection molding. The invention also concerns a device for carrying out the method and a brush comprising corresponding bristles.
Animal hair and natural fibers which were previously used as bristle material for producing brushes, paint brushes or the like have been substantially replaced by plastic bristles, wherein the production of the bristle material is based largely on the well established production of synthetic textile fibers, i.e. extrusion or spinning processes. However, a bristle is subjected to completely different conditions than an endless fiber in a fiber composite. It is free and fixed at only one end and can be regarded in terms of stability as a freely projecting bar which bends and which is fixed at one end. Pressure or compression forces and sometimes also tensile forces occur during use. Compared to endless fibers, the stability requirements are different with regard to bending strength, fatigue strength under reversed bending stresses, buckling resistance and bend recovery.
Corresponding bristles can be used for toothbrushes, cleaning brushes or brooms in particular in the field of hygiene, applicators for powdery or liquid media, in particular liquids, cleaning agents, solvents, paints and varnishes and cosmetics, for application pads, cleaning pads including mats for cleaning shoes, combs, hairbrushes pr technical brushes. By way of example, bristles for a toothbrush are described below. The invention is however not limited thereto.
As has been known for a long time, the cleaning effect of a toothbrush can be improved by providing a structure or profile on the outer surface of the bristle. If the bristles are e.g. provided on their outside with wart-like nubs (DE 100 17 167.2) or ribs (U.S. Pat. No. 1,773,969) the plaque removing effect on the tooth can be increased by up to 50%.
Such bristles having a structure or profile on their outer side are usually produced in the desired cross-sectional shape by extrusion or are surface-formed under continuous processing following production as an unprofiled monofilament. Profiling improves the brushing and cleaning effect but has the disadvantage that the profiling impairs the stability properties of the bristle in its mounting region and the bristle tends to bend or kink.
The known externally profiled bristles also have negative effects on hygiene. Due to the profiling, chambers and undercuts are formed on the bristle proximate to and, in particular, in its fixing region in which impurities may deposit which cannot be removed or which can only be removed to an inappropriate degree due to the densely packed bristle field. This can produce fungal, bacterial and microbial growth.
To increase the brushing and cleaning effect of a bristle, U.S. Pat. No. 3,256,545 and U.S. Pat. No. 4,167,794 suggest providing a widened head at the free end of the bristle, which protrudes laterally by an amount corresponding to several times the diameter of the cylindrical bristle stem. In this design, the fixing region is loaded with high bending moments due to the mass and the brushing resistance of the head, which may cause the bristle to kink even after a short time of use thereby rendering the bristle unusable.
It is the underlying purpose of the present invention to produce a bristle of the above-mentioned type which is hygienically impeccable, strong, efficient and highly stable for a long period of time. The invention should moreover produce a brush comprising corresponding bristles and propose a method for producing a corresponding bristle through casting and in particular injection molding whose bending behavior and bend recovery exceed that of extruded bristles, while permitting optimum realization of the theoretical elasticity values and tensile strengths and which permits production of bristles of high quality over large length ranges even with relatively small cross-sections to be able to produce bristle geometries and bristle arrangements in a simple fashion while thereby adjusting the brushes and paint brushes to the requirements of the final product. The invention is moreover based on providing a device, which is suitable for carrying out the method.